Set of faces to manage instrumentation listeners, data and probes

Here are 3 faces to manipulate more easily the various instrumentation
indirections:

• instrumentation_listener

This allows to enable/disable and list the registered listeners

• instrumentation_data

This allows to retrieve a given listener accumulated data

• instrumentation_probe

This allows to list the various probes of a given system, and
enable or disable them.

Note: for the probe face to work, one need the fix for

Signed-off-by: Brice Figureau <brice-puppet@daysofwonder.com>